1. Field of the Invention
The present invention relates to a leadframe for packaging a semiconductor device and, more particularly, to a leadframe having slots in a die pad.
2. Description of the Related Art
As shown in FIG. 1, a conventional leadframe 1 comprises a die pad 11 and a plurality of pins 12, 13. The die pad 11 is used for receiving a die. In a conventional packaging technique for a power transistor, for the purpose of dissipating heat from the power transistor, the area of the die pad 11 is usually made larger than that of the die.
Referring to FIG. 2, the die pad 11 receives a die 2, and the die 2 is connected to the die pad 11 with die-attach material 3 commonly consisting of tin solder paste or silver epoxy. When the die-attach material 3 is solder paste, the solder paste 3 must be heated during the packaging process. In the heating process, the solder paste 3 expands on the die pad such that the die 2 on the solder paste 3 drifts or rotates due to the movement of the melted solder paste 3. Therefore, the die 2 cannot be positioned precisely on the die pad 11. This lowers the quality of packaging the semiconductor device.
Therefore, it is desirable to provide a creative and improved die pad of a leadframe to overcome the above problem.
One objective of the present invention is to provide a die pad of a leadframe. The die pad is used for receiving a die. The die and the die pad are connected together by solder paste. The die pad has a plurality of slots that penetrate through the die pad. A restrictive region is formed between the slots such that the solder paste is restricted to the restrictive region. The die can be positioned on the restrictive region. Because of the cohesion of the solder paste, the solder paste does not flow into the slots. Therefore, the solder paste does not flow and expand everywhere during the heating process. The solder paste is restricted to the restrictive region so that the die on the solder paste does not shift or rotate, thereby increasing the packaging quality.